Update dev build to include old and new system.valuetuple

[KevinRansom]

In a recent overhaul of the build. We updated to 4.4.0 of the System.ValueTuple nuget package.

We also updated the templates to support this newer nuget package.

However, the templates with the VS2017.6 and VS2017.7 previews require the 4.3.1 nuget package. This PR amends developer builds so that they will deploy both the 4.3.1 and 4.4.0 System.ValueTuple, when the template is created.

Note: When VSIX installs a nuget package, it doesn't really go to nuget and install it. It sort of fake drops files.

This change is only intended to impact developer builds, internal product builds will only deploy the correct version.

@brettfo can you confirm that microbuild is set for internal builds.

[brettfo]

can you confirm that microbuild is set for internal builds.

Yes, it is. The official signed build definition does this:

[brettfo]

Alternately we already set the environment variable %CI%/$(CI) to 1, but I'm OK with either.